Multi-layer reflection mirror for soft X-ray to vacuum ultraviolet ray

ABSTRACT

A multi-layer reflection mirror for soft X-ray to vacuum ultraviolet ray, comprises a substrate, a plurality of first layers, and a plurality of second layers formed on the substrate alternately with the first layers. The first layers primarily consists of at least one of single elements, such as ruthenium, or of a boride carbide, silicate, nitride oxide of a transition metal. The second layers primarily consists of at least one of compounds of carbon, silicon (e.g. carbide, nitride and oxide of silicon), boron (e.g. carbide, nitride and oxide of boron), beryllium (e.g. carbide, nitride and oxide of beryllium) and aluminum (e.g. carbide, nitride and oxide of aluminum).

This application is a continuation of application Ser. No. 08/086,367filed Jul. 6, 1993, now abandoned, which is a continuation ofapplication Ser. No. 07/844,285 filed Mar. 2, 1992 now abandoned whichis a division of 07/602,922 filed Oct. 25, 1990 now abandoned which is acontinuation of application Ser. No. 07/246,012 filed Sep. 14, 1988, nowabandoned, which is a continuation of application Ser. No. 07/102,498filed Sep. 29, 1987, now abandoned.

BACKGROUND OF THE INVENTION

The present invention relates to a multilayer reflection mirror for softX-ray to vacuum ultraviolet ray used for incidence of light having awavelength of less than 200 nm which is called soft X-ray to vacuumultraviolet ray, at an incident angle closely perpendicular to a mirrorsurface.

In the past, there has been no reflection mirror having a high(reflectivity) for a light having a shorter wavelength than an areacalled the vacuum ultraviolet which is directed perpendicularly orclosely perpendicularly to the mirror plane, and a reflection factor hasbeen less than 1% for the incident angle close to the perpendicularincident angle. In an oblique incident reflection mirror which has arelatively high reflection factor, it is necessary to adjust theincident angle between 1° and 2°-3° relative to the mirror plane.Because the light has to be directed to the plane with a very smallangle, a very large size mirror is required even for a fine light beamand the use thereof is difficult, and limited freedom of design of theoptical system, and the face that reflection mirror must be polished inorder to have a high degree of planarity over a wide area makes the usethereof difficult.

As vacuum evaporation techniques have advanced recent years, amulti-layer reflection mirror having a number of super-thin filmslaminated have been manufactured, and the reflection mirror having ahigh reflection factor by the use of interference has been put intopractice.

In the area of X-ray and vacuum ultraviolet ray, refractive indices ofmost materials are represented by complex refractive indices (n+ik,hereinafter called refractive indices) having imaginary number portionsk representing absorption, and real number portions n beingsubstantially equal to 1.0 (n=1-δ, δ, ≃10⁻¹ -10⁻³). Accordingly, aFlesnel reflection factor at a boundary of vacuum and material thin filmis very small, that is, in the order of 0.1% or less, The reflectionfactor does not exceed several % per boundary plane ever at a boundaryof laminated thin films of heterogeneous materials. By alternatelylaminating heterogeneous materials to form a multi-layer laminatedstructure so that reflected lights from the respective layer boundariesenhance each other by interference a reflection factor of the entiremulti-layer film is maximized and, a high reflection factor is thusattained. By selecting a combination of heterogeneous materials whichresults in a big difference between refractive indices of adjacentlayers to attain a high reflection factor together with the multi-layerfilm structure, a reflection mirror which has a high reflection factorat an incident angle close to a normal incident angle is attained.

In known combinations of materials, a transition metal element having ahigh melting point is used as a material for a low refractive indexlayer, and a semiconductor element such as carbon or silicon is used asa material for a high refractive index layer. Typical examples arecombinations of tungsten (W) and carbon (C) and combinations ofmolybdenum (Mo) and silicon (Si). (See S. V. Gaponor et al, Optics Comm.38 (1981), 7; T. W. Barbee et al, App. Opt. 24 (1985), 883).

When a high intensity light such as a synchrotron track radiation lightis applied to a reflection mirror having such a combination, thereflection mirror is locally heated and the multi-layer structure willbe readily broken if the high refractive index layer has a low meltingpoint (for example, Si).

In order to avoid the above problem, the low refractive index metallayer having a high melting point may be used, but a metal single bodyusually has a melting point of around 2500° C. (for example, Mo/Si) anda metal having a melting point of 3000° C. or higher (for example, W/C)does not attain a high reflection factor.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a reflection mirrorwhich eliminates the above problems, retains a high reflectioncoefficient, has a high heat resistance and minimizes diffusion betweenlayers.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a diagram of an embodiment of a multi-layer reflectionmirror for soft X-ray to vacuum ultraviolet ray.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The above object of the present invention is achieved in the embodiments1, 2 and 3 by the multilayer reflection mirror for soft X-ray to vacuumultraviolet ray having a multi-layer thin film structure of alternatehigh refractive index layers and low refractive layers for soft X-ray tovacuum ultraviolet ray, wherein the low refractive index layer primarilyconsists of one or more single element of transition metals and the highrefractive index layer primarily consists of one or more of carbide,nitride or oxide of silicon or boron.

FIG. 1 shows a diagram of one embodiment of the multi-layer reflectionmirror for soft X-ray to vacuum ultraviolet ray of the presentinvention.

The multi-layer reflection mirror shown in FIG. 1 has a planar or curvedsubstrate 1 polished sufficiently smoothly relative to a wavelength used(for example, surface roughness rms is 10 Å or less) on which first lowrefractive index layers 2, 4, 6, . . . and second high refractive indexlayers 3, 5, 7, . . . are alternately laminated.

The low refractive index layer of the embodiments 1, 2 and 3 primarilyconsists of one or more of single elements of transition metal.

The transition metal used in the present invention is an element havingelectron vacancies in 3d, 4d and 5d tracks such as scandium (Sc),titanium (Ti), vanadium (V), chromium (Cr), iron (Fe), nickel (Ni),cobalt (Co), zirconium (Zr), niobium (Nb), molybdenum (Mo), technetium(Tc), ruthenium (Ru), rhodium (Rh), hafnium (Hf), tantalum (Ta),tungsten (W), rhenium (Re), osmium (Os), iridium (Ir), platinum (Pt), orcopper (Cu), palladium (Pd), silver (Ag) or gold (Au) having 3d, 4d and5d tracks filled with electrons.

The high refractive index layer in the embodiments 1, 2 and 3 primarilyconsists of one or more of carbide, nitride or oxide of silicon, boron,berylium or aluminum. Specifically, the carbide is silicon carbide (SIC)or boron carbide (B₄ C), the nitride is silicon nitride (Si₃ N₄) orboron nitride (BN), and the oxide is silicon monoxide (SiO) or silicondioxide (SiO₂). One of those compounds or a mixture of two or more ofthem constitutes the high refractive index layer.

Film thicknesses d₁, d₂, . . . of the respective layers are larger than1/4 of the wavelength used and alternate layers are of the samematerial. The film thickness is determined by having to balancesatisfying a condition in which all reflected lights from boundaries ofthe layers interfere to enhance each other as well as satisfying acondition in which reduction of a total reflection factor is smallerthan reduction of a reflection factor due to an absorption loss by anabsorber and a phase shift. For example, the film thicknesses of thesame material layers may be equal for easiness of manufacture, or thefilm thickness may be adjusted for each layer to maximize the reflectionfactor.

The material of the laminated layer is preferably selected such that therefractive index of an outermost layer which faces air has a bigdifference from the refractive index of air in order to attain a highreflection factor. To this end, the low refractive index layer ispreferably the outermost layer. It is also desirable that a differencebetween a refractive index of the substrate and a refractive index ofthe layer adjacent to the substrate is big.

The reflection mirror of the present invention includes a two-layerstructure having one high refractive index layer and one low refractiveindex layer but ten or more layered structure is preferable because thegreater the number of alternate layers is, the higher is the reflectionindex. However, since the absorption significantly increases if thenumber of layers is too large, up to 200-layer structure is preferablefor ease of manufacture. A protective layer of a low absorption andstable material may be formed on the outermost layer.

In order to manufacture the multi-layer reflection mirror for soft X-rayto vacuum ultraviolet ray of the present invention, electron beam vapordeposition in ultra-high vacuum or sputtering method in vacuum havingsufficiently low amount of residual oxygen where compound material isused may be effectively utilized. Alternatively, resistive heating vapordeposition, CVD, reactive sputtering or other thin film forming methodmay be used.

The multi-layer reflection mirror for soft X-ray to vacuum ultravioletray of the present invention is usually formed on a substrate of glass,molten quartz, silicon single crystal or silicon carbide having asurface thereof polished sufficiently smoothly relative to thewavelength used.

The embodiments 1, 2 and 3 will be explained in further detail.

Embodiment 1

On a silicon carbide (SIC) substrate 1 optically polished to have asurface precision of λ/20 (λ=6328 Å) and surface roughness of 10 Å(rms), ruthenium (Ru) low refractive index layers 2, 4, . . . eachhaving a thickness of 34.3 Å and silicon dioxide (SiO₂) high refractiveindex layers 3, 5, . . . each having a thickness of 31.0 Å werelaminated to form a 41-layer structure (Ru: 21 layers, SiO₂ : 20layers). The outermost layer of the lamination was ruthenium layer, anda carbon (C) protective film 10 having a thickness of 5 Å was formedthereon to complete the multi-layer reflection mirror for soft X-ray tovacuum ultraviolet ray.

Both the ruthenium layers and the silicon dioxide layers were formed bythe electron beam vapor deposition in a ultra-high vacuum (below 1×10⁻⁷Pa). The vapor; deposition rate was 0.2 Å/s for both materials. Theprotective layer was formed by the electron beam vapor deposition.

When a light having a wavelength of 124.0 Å was directed normally to themulti-layer reflection mirror for soft X-ray to vacuum ultraviolet ray,a reflection factor of 54.7% was attained. A similar multi-layerreflection mirror for soft X-ray to vacuum ultraviolet ray having 41laminated layers with the thickness of ruthenium layer being 36.8 Å, thethickness of silicon dioxide layer being 33.2 Å and the thickness ofcarbon protective layer being 5 Å was formed. When a light was directedthereto at an incident angle of 20 degrees with respect to a normalline, a reflection factor of 56.4% was attained.

Embodiment 2

On a polished silicon substrate, tantalum (Ta) low refractive indexlayers 2, 4, . . . each having a thickness of 19.9 Å and boron carbide(B₄ C) high refractive index layers 3, 5, . . . each having a thicknessof 44.1 Å were laminated to form a 101-layer structure (Ta: 51 layers,B₄ C: 50 layers). The outermost layer of the lamination was the tantalumlayer, and a carbon protective layer 10 having a thickness of 10 Å wasformed thereon to complete the multi-layer reflection mirror for softX-ray to vacuum ultraviolet ray.

Both the low refractive index layers and the high refractive indexlayers were formed by the electron beam vapor deposition in a ultra-highvacuum (below 1×10⁻⁷ Pa). The vapor deposition rate was 0.2 Å/s for bothmaterials.

When a light having a wavelength of 124.0 Å was directed normally to themulti-layer reflection mirror for soft X-ray to vacuum ultraviolet ray,a reflection factor of 12.7% was attained.

A similar multi-layer reflection mirror having a 101-layer structurewith the thickness of the low refractive index layer being 21.0 Å andthe thickness of the high refractive index layer being 47.7 Å wasformed. When a light having a wavelength of 124.0 Å was directed theretoat an incident angle of 20° with respect to a normal line, a reflectionfactor of 12.9% was attained.

Embodiment 3

On a polished molten (fused) quartz substrate, hafnium (Hf) lowrefractive index layers 2, 4, . . . each having a thickness of 25.5 Åand silicon nitride (Si₃ N₄) high refractive index layers 3, 5, . . .each having a thickness of 36.8 Å were laminated to form a 41-layerstructure (Hf: 21 layers, Si₃ N₄ :20 layers). The outermost layer of thelamination was the hafnium low refractive index layer, and a carbonprotective film 10 having a thickness of 10 Å was formed thereon tocomplete the multi-layer reflection mirror for soft X-ray to vacuumultraviolet ray of the present invention.

Both the high refractive index layers and the low refractive indexlayers were formed by the electron beam vapor deposition in theultrahigh vacuum (below 1×10⁻⁷ Pa). The vapor deposition rate was 0.2Å/s for both materials.

When a light having a wavelength of 124.0 Å was directed normally to themulti-layer reflection mirror for soft X-ray to vacuum ultraviolet-ray,a reflection factor of 13.7% was attained.

A multi-layer reflection mirror having a 41-layer structure with thethickness of the low refractive index layer being 26.6 Å and thethickness of the high refractive index layer being 39.7 Å was formed.When a light having a wavelength of 124.0 Å was directed thereto at anincident angle of 20° with respect to the normal line, a reflectionfactor of 14.6% was attained.

The above object of the present invention is achieved in embodiments 4,5 and 6 by the multi-layer reflection mirror for soft X-ray to vacuumultraviolet ray having a multi-layer thin film structure of alternatehigh refractive index layers and low refractive index layers for softX-ray to vacuum ultraviolet ray, wherein the low refractive index layerprimarily consists of one or more of boride, carbide or silicate oftransition metal and the high refractive index layer primarily consistsof one or more of single elements of carbon, silicon, boron or berylliumor compounds thereof.

In those embodiments, the low refractive index layer primarily consistsof one or more of boride, carbide, silicide, nitride or oxide of atransition metal.

In those embodiments, the compounds of the transition metal includeboride such as tantalum boronide, hafnium boride, tungsten boride orniobium boride; carbide such as tantalum carbide, hafnium carbide,tungsten carbide or niobium carbide; silicide such as tantalum silicide,tungsten silicide or palladium silicide; nitride such as tantalumnitride, hafnium nitride, tungsten nitride or niobium nitride; and oxidesuch as tantalum oxynitride.

In those embodiments, the low refractive index layer may consist of oneof-carbide, nitride or boride of the transition metal or two or morematerials such as tantalum nitride (TAN) and niobium nitride (NbN) ofany proportion.

The high refractive index layer primarily consists of one or more ofsingle elements of carbon, silicon, boron or beryllium or compoundsthereof such as silicon carbide and boron carbide.

The embodiments 4, 5 and 6 will be explained below in further detail.

Embodiment 4

On a silicon single crystal substrate 1 optically polished to have asurface precision of λ/20 (λ=6328 Å) and a surface roughness of 10 Å(rms), hafnium boride (HfB₂) low refractive index layers 2, 4, . . .each having a thickness of 22.4 Å and beryllium (Be) high refractiveindex layers 3, 5, . . . each having a thickness of 33.5 Å werelaminated to form a 41-layer structure (21 HfB₂ layers and 20 Belayers). The outermost layer of the lamination was the hafnium boridelayer, and a carbon (C) protective layer 10 having a thickness of 10 Åwas formed thereon to complete the multi-layer reflection mirror forsoft X-ray to vacuum ultraviolet ray of the present invention.

Since hafnium boride has a high melting point, 3250° C. the film thereofwas formed by the electron beam vapor deposition in the ultra-highvacuum (below 1×10⁻⁷ Pa). Since beryllium (Be) has a relatively lowmelting point (-1300° C.), the film thereof was vapor-deposited by theresistive heating method. The vapor deposition rate was 0.2 Å/s for bethmaterials. The protective layer was formed by the electron beam method.

When a light having a wavelength of 112.7 Å was directed normally to themulti-layer reflection mirror for soft X-ray to vacuum ultraviolet ray,a reflection factor of 31.3% was attained. A similar multi-layerreflection mirror having a 41-layer structure was formed, with thehafnium boronide layer being 23.2 Å thick, the beryllium layer being36.2 Å thick and the carbon protective layer being 10 Å thick. When thelight was directed thereto at an incident angle of 20° with respect to anormal line, a reflection factor of 34.3% was attained.

Embodiment 5

On a polished silicon substrate similar to that of the embodiment 4,tantalum nitride (TAN) low refractive index layers 2, 4, . . . eachhaving a thickness of 20.0 Å and silicon (Si) high refractive indexlayers 3, 5, . . . each having a thickness of 40.8 Å were laminated toform a 41-layer structure (21 TaN layers and 20 Si layers). Theoutermost layer of the lamination was the tantalum nitride, layer, and acarbon protective layer 10 having a thickness of 10 Å was formed thereonto complete the multi-layer reflection mirror for soft X-ray to vacuumultraviolet ray of the present invention.

The high melting point tantalum nitride film was formed by the electronbeam vapor deposition in the ultra-high vacuum (below 1×10⁻⁷ Pa). Thehigh refractive index silicon film was formed in a similar manner. Thevapor deposition rate was 0.2 Å/s for both materials.

When a light having a wavelength of 124.0 Å was directed normally to themulti-layer reflection mirror for soft X-ray to vacuum ultraviolet ray,a reflection factor of 42.5% was attained.

A multi-layer reflection mirror having a 41-layer structure was formed,with the low refractive index layer being 20.5 Å thick and the highrefractive index layer being 44.0 Å thick. When a light having awavelength of 124.0 Å was directed thereto at an incident angle of 20°with respect to a normal line, a reflection factor of 44.7% wasattained.

Embodiment 6

On a silicon substrate polished in the same manner as the embodiment 4,tungsten carbide (W₂ C) low refractive index layers 2, 4, . . . eachhaving a thickness of 21.1 Å and silicon (Si) high refractive indexlayers 3, 5, . . . each having a thickness of 39.8 Å were laminated toform a 41-layer structure (21 W₂ C layers and 20 Si layers). Theoutermost layer of the lamination was the low refractive index tungstencarbide layer. A carbon protective layer 10 having a thickness of 10 Åwas formed thereon to complete the multi-layer reflection mirror forsoft X-ray to vacuum ultraviolet ray of the present invention.

The high melting point tungsten carbide film was formed by the electronbeam vapor deposition in the ultra-high vacuum (below 1×10⁻⁷ Pa). Thehigh refractive index silicon film was formed in the same manner. Thevapor deposition rate was 0.2 Å/s for both materials.

When a light having a wavelength of 124.0 Å was directed normally to themulti-layer reflection mirror for soft X-ray to vacuum ultraviolet ray,a reflection factor of 42.8% was attained.

A multi-layer reflection mirror having a 41-layer structure was formed,with the low refractive index layer being 21.7 Å thick and the highrefractive index layer being 42.9 Å thick. When a light having awavelength of 124.0 Å was directed thereto at an incident angle of 20°with respect to a normal line, a reflection factor of 45.1% wasattained.

The above object of the present invention is achieved in embodiments 7and 8 by the multi-layer reflection mirror for soft X-ray to vacuumultraviolet ray having alternate layers of two different refractiveindices, wherein the materials of the layers are made of high meltingpoint compounds. In this method, the materials of the layers are stablefor heat and also chemically stable. Accordingly, the peel-off of thelayer or diffusion between layers during heating of the multi-layerstructure is prevented.

In the embodiments 7 and 8, the materials of the layers are high meltingpoint compounds so that the performance of the reflection mirror ismaintained even if it is locally heated by a high intensity light suchas synchrotron track radiation light. Such materials may be compoundshaving a melting point of 2000° C. or higher, such as aluminum nitride(AlN), beryllium nitride (Be₃ N₂), titanium nitride (TIN), niobiumnitride (NbN), vanadium nitride (VN), zirconium nitride (ZrN), boronnitride (BN), hafnium nitride (HfN), tantalum nitride (TAN, Ta₂ N),aluminum boride (AlB₁₂), titanium boride. (TiB₂), vanadium boride (V₃B₄, VB), tungsten boride (WB), hafnium boride (HfB₂), zirconium boride(ZrB₂), boron carbide (B₄ C), molybdenum carbide (Mo₂ C), berylliumcarbide (Be₂ C), silicon carbide (SIC), vanadium carbide (V₂ C),tungsten carbide (WC, W₂ C), hafnium carbide (HfC), niobium carbide(NbC), tantalum carbide (TaC), titanium carbide (TIC), zirconium carbide(ZrC), aluminum oxide (Al₂ O₃), beryllium oxide (BeO), chromium oxide(Cr₂ O₃), hafnium oxide (HFO₂), titanium oxide (Ti₂ O₃), cerium oxide(CeO₂) and zirconium oxide (ZrO₂).

The two materials are selected from the above materials and alternatelylaminated such that Δn=|n₁ -n₂ |≧10⁻³, where n₁ =n₁ +ik₁ is a retractiveindex of the material of the first layer and n₂ =n₂ +ik₂ is a refractiveindex of the material of the second layer. If Δn=|n₁ -n₂ |<10⁻³ thecombination may be such that it satisfies |k₁ -k₂ |>Δn. In this manner,a high reflection factor is attained.

In those embodiments, the reflection factor of the multi-layerreflection mirror for soft X-ray to vacuum ultraviolet ray depends onthe difference between the refractive indices of the two alternatelayers, absorption rates of the layers, the number of layers laminatedand the wavelength of the irradiated light. The difference between therefractive indices of the two materials is preferably at least 0.01 whenthe number of layers is 100 pairs.

In order to give a difference between the refractive indices of thealternate layers, high refractive coefficient material and lowrefractive index material for a light in the range of X-ray to vacuumultraviolet ray may be alternately laminated. The low refractive indexand high melting point material may be boride, nitride, carbide or oxideof transition metal, and the high refractive index and high meltingpoint material may be nitride, carbide or oxide of beryllium, aluminum,boron or silicon.

The embodiments 7 and 8 are explained below in further detail.

Example 7

On a silicon substrate 1 coated with silicon carbide (SIC) opticallypolished to have a surface precision of λ/20 (λ=6328 Å) and a surfaceroughness of 7 Å(rms), hafnium nitride (HfN) low refractive index layers2, 4, . . . each having a thickness of 23.0 Å and silicon carbide (SIC)high refractive index layers 3, 5, . . . each having a thickness of 38.8Å were alternately laminated to form a 41-layer structure (21 HfN layersand 20 SiC layers). The outermost layer of the lamination was thehafnium nitride layer, and a carbon (C) protective layer A having athickness of 10 Å was formed thereon. Both the hafnium nitride layersand the silicon carbide layers were deposited by the electron beam vapordeposition in the ultra-high vacuum (<10⁻⁶ Pa). The vapor depositionrate was 0.2 Å/sec for both materials. The protective layer was formedby the electron beam method.

When a light having a wavelength of 124.0 Å was directed normallythereto, a reflection factor of 29.8% was attained.

Another multi-layer reflection mirror having the hafnium nitride layerthickness of 23.8 Å and the silicon carbide layer thickness of 41.9 Åwas formed. When the light having a wavelength of 124.0 Å was directedthereto at an incident angle of 20°, a reflection index of 31.5% wasattained.

Embodiment 7

On a silicon substrate coated with silicon carbide of 100μ thickpolished in the-same manner as the embodiment 7, tantalum nitride (TAN)low refractive index layers 2, 4, . . . each having a thickness of 21.7Å and silicon carbide (SIC) high refractive index layers 3, 5, . . .each having a thickness of 40.1 Å were alternately laminated to form a41-layer structure (21 TaN layers and 20 SiC layers). The outermostlayer of the lamination was the tantalum nitride having a largerefractive index difference from vacuum, and a carbon protective layer Ahaving a thickness of 10 Å was formed thereon. Both the low refractiveindex layers and the high refractive index layers were formed by theelectron beam vapor deposition in the ultra-high vacuum (below 10⁻⁶ Pa).The vapor deposition rate was 0.2 Å/sec for both materials. When a lighthaving a wavelength of 124.0 Å was directed. normally thereto, areflection factor of 31.3% was attained.

Another multi-layer reflection mirror of a 41-layer structure with thetantalum nitride layer thickness of 22.1 Å and the silicon carbide layerthickness of 43.5 Å was formed. When the light having a wavelength of124.0 Å was directed thereto at an incident angle of 20° with respect toa normal line, a reflection factor of 32.8% was attained.

Comparative Example

(Sold (Au) was used for the low refractive index layers and carbon (C)was used for the high refractive index layers, and a multi-layerreflection mirror for soft X-ray to vacuum ultraviolet ray wasmanufactured by the electron beam vapor deposition method in a similarmanner to that of the embodiment 1.

The reflection mirror was mounted on a soft X-ray spectrometer whichused a synchrotron track radiation light (SR) and it was subjected tothe radiation light for total of five hours. Cracks and peel-off of thefilms were observed. The multi-layer reflection mirrors manufactured inthe Embodiments 1, 2, 3, 4, 5 and 6 were mounted on the spectrometer andsubjected to the radiation for the same time. No damage was observed.

The multi-layer reflection mirror for X-ray to vacuum ultraviolet ray ofthe present invention has a high reflection factor to the light in therange of soft X-ray to vacuum ultraviolet ray and has a sufficientlylong durability compared to the prior art reflection mirror which issubstantially damaged in a short time by the irradiation of thesynchrotron track radiation light (SR).

By combining a plurality of planar or curved reflection mirrors, areduction/enlarge optical system for X-ray, a reflection mirror for alaser resonator in a range of soft X-ray to vacuum ultraviolet ray, anda reflection type dispersion element with a grid-structure reflectionmirror, which have not been available hithertofore in the range ofX-ray, are provided and an application range of the optical elements isexpanded.

We claim:
 1. A multi-layer reflection mirror for soft X-ray to vacuumultraviolet ray, comprising:a plurality of first layers, each of saidfirst layers, comprising ruthenium as a main constituent thereof; aplurality of second layers, each of said second layers being alternatelylayered to each of said first layers, each of said second layerscomprising silicon dioxide as a main constituent thereof; and asubstrate supporting said first and second layers, said substrateselected from the group consisting of glass, quartz, silicon singlecrystal and silicon carbide having a surface roughness of less than 10 Å(rms).
 2. A reflection mirror according to claim 1, wherein saidreflection mirror reflects a synchrotron radiation.
 3. A reflectionmirror for soft X-ray to vacuum ultraviolet ray, comprising:a substrateselected from the group consisting of glass, quartz, silicon singlecrystal and silicon carbide having a surface roughness of less than 10 Å(rms); and a multi-layer film formed on said substrate, said multi-layerfilm having a plurality of first layers and a plurality of secondlayers, each of said second layers being alternately layered to each ofsaid first layers on said substrate, each of said first layers comprisesas a main constituent thereof one single element of a transition metal,each of said second layers comprising at least one nitride and at leastone oxide selected from the group consisting of boron and silicon.
 4. Areflection mirror according to claim 3, wherein said substrate comprisessilicon carbide.
 5. A reflection mirror according to claim 3, whereinsaid first layers comprise hafnium and said second layers comprisesilicon nitride.
 6. A reflection mirror according to claim 5, whereinsaid substrate comprises molten quartz.
 7. A reflection mirror accordingto claim 3, wherein said reflection mirror reflects a synchrotronradiation.
 8. A reflection mirror according to any one of claim 3through 6, wherein said substrate has a planar surface.
 9. A multi-layermirror for soft x-ray to vacuum ultraviolet ray, comprising:a substrateselected from the group consisting of glass, quartz, silicon singlecrystal and silicon carbide; and a multi-layer film formed on saidsubstrate, said multi-layer film having a plurality of first layers anda plurality of second layers, each of said second layers beingalternately layered to each of said first layers on said substrate, eachof said first layers comprising as a main constituent thereof one singleelement of a transition metal, each of said second layers comprising atleast one silicon nitride or silicon oxide, and a carbon layer formed onsaid multi-layer film.
 10. A multi-layer mirror according to claim 9,wherein said multi-layer mirror reflects a synchrotron radiation.
 11. Amulti-layer mirror according to claim 9, wherein said substrate has aroughness of less than 10 rms.